Feature sizes for integrated circuits are continuously being reduced in response to many factors, including demand for increased portability, computing power, memory capacity and energy efficiency. Reduced feature sizes for integrated circuits are related to the techniques used to form said features. For example, lithography is commonly used to pattern features (e.g., conductive lines) of integrated circuits. The periodicity of these patterned features maybe described as a pitch.
Pitch describes the distance between identical points of two neighboring features. Lithographic techniques cannot reliably form features below a minimum pitch due to factors such as optics and light or radiation wavelength. Thus, the minimum pitch of a lithographic technique is an obstacle to feature size reduction.
Techniques to extend the capabilities of lithographic techniques beyond their minimum pitch are referred to as pitch division, or pattern density multiplication, techniques. For example, when a pitch is halved, this reduction is referred to as pitch doubling, and when a pitch is quartered, this reduction is referred to as pitch quadrupling or pitch quad.
Prior art pitch quad techniques typically require line reduction to be finalized prior to transferring a pattern to a hard mask layer. Furthermore, if feature size is shrunk below 15 nm, the physical strength of the feature may not be enough to withstand processing environments. Pitch quad lines produced by prior art methods are susceptible to feature collapse due to capillary forces (e.g., moisture in the air, fluid processing) and shorting problems (because of the reduced space between the lines).
The descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the invention is provided below, followed by a more detailed description with reference to the drawings.